Photographic elements,compositions and processes

ABSTRACT

A DEVELOPING AGENT PRECURSOR WHICH IS A REACTION PRODUCT OF (A) A 3,4-DIHYDROXY FURAN SILVER HALIDE DEVELOPING AGENT, SUCH AS ASCORBIC ACID, OR A HYDROXYTETRONIC ACID SILVER HALIDE DEVELOPING AGENT, SUCH AS 5-PHENYL-3HYDROXYTETRONIC ACID, WITH (B) A BASIC AMINOPHENOL SILVER HALIDE DEVELOPING AGENT IS EMPLOYED IN PHOTOGRAPHIC ELEMENTS, COMPOSITIONS AND PROCESSES, ESPECIALLY DRY PROCESSING WITH HEAT. SUCH A DEVELOPING AGENT PRECURSOR HAS THE PROPERTY OF BEING HEAT ACTIVATED IN THE ABSENCE OF ALKALI.

United States Patent 3,600,176 PHOTOGRAPHIC ELEMENTS, COMPOSITIONS ANDPROCESSES Grant M. Haist and David A. Pupo, Rochester, N.Y., assignorsto Eastman Kodak Company, Rochester,

Nb brawin Filed Nov. 29, 1968, Ser. No. 780,231 1m. c1. G03c 5/30 US.or. 96-66 16 Claims ABSTRACT OF THE DISCLOSURE A developing agentprecursor which is a reaction product of (a) a 3,4-dihydroxy furansilver halide developing agent, such as ascorbic acid, or ahydroxytetronic acid silver halide developing agent, such as 5-phenyl-3-hydroxytetronic acid, with (b) a basic aminophenol silver halidedeveloping agent is employed in photographic elements, compositions andprocesses, especially dry processing with heat. Such a developing agentprecursor has the property of being heat activated in the absence ofalkali.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to developing agent precursors and to photographic systemscontaining such precursors. In one of its aspects, the invention relatesto elements containing these developing agent precursors. In another ofits aspects it relates to photographic compositions, especiallyphotographic silver halide emulsions, containing the describeddeveloping agent precursors. A further aspect comprises a method ofdeveloping a latent image in a photographic element employing dryprocessing with heat. It also relates to photographic developerprecursor compositions, especially aqueous solutions which are activatedby heat.

Description of the prior art In the usual process of photographicdevelopment in an exposed photographic element comprising a supporthaving at least one photographic silver halide layer is immersed in adeveloping bath containing a silver halide developing agent. Developingbaths of the prior art normally contain a developing agent, apreservative, such as sodium sulfite, a development activator, such asalkali to activate the developing agent, and can also contain othermaterials, such as sodium bromide as a restrainer, antifoggants and thelike.

Incorporation of silver halide developing agents in layers ofphotographic elements is also known. These are developed after exposure,typically by treating them in alkaline solutions, which may or may notcontain a developing agent. Following development the developed silverimage can be fixed, washed and dried.

The processes employed to develop these emulsions have been referred toas Wet processes. Such processes are described, for example, in Mees,The Theory of the Photographic Process, 3rd edition (1966), pp. 278311.

The use of light sensitive silver halide emulsion layers which contain adeveloping agent and in which the latent image can be developed by heatprocessing are also known. These materials usually have the advantage ofbeing processed simply and rapidly without the use of solutions. Suchprocesses have been referred to as dry processes, since no liquidprocessing solutions are required in the development of the photographicimage. One process of this type employs the reaction product of analkaline developing agent, such as p-aminophenol with a readilydecarboxylated organic acid. This reaction prod- 3,600,176 Patented Aug.17, 1971 uct is incorporated in a photographic element, and a free basedeveloping agent is produced upon heating to decarboxylation temperatureas described in US. Pat. 3,220,846 of Tinker and Sagura issued Nov. 30,1965. The use of developing agents such as ascorbic acid and 1-phenyl-3-pyrazolidone in photographic elements for dry processing whichare subjected to heat are also disclosed in US. Pat. 3,041,170 of Haistand King issued June 26, 1962. Mixtures of hydroquinone with 1-phenyl-3-pyrazolidone or ascorbic acid with 1-phenyl-3-pyrazolidone inphotographic elements for dry processing are also disclosed in BritishPat. 930,572 published July 3, 1963. Combinations of ascorbic aciddeveloping agents with 3-pyrazolidone developing agents are furtherdisclosed in British Pat. 778,792; French Pat. 1,500,987 and French Pat.1,500,988.

Acidic materials such as ascorbic acid, gallic acid and the like havebeen employed as photographic silver halide developing agents. However,the employment of such acids as silver halide developing agents inphotographic coatings, such as silver halide emulsions can result inunstable photographic elements that in many cases cannot be suitablystored and lose desired sensitometric properties.

On the other hand, attempts to employ free base developing agents, suchas N-methyl-p-aminophenol in its free base form, provides an unsuitablephotographic coating. These are ordinarily neutralized with a strongacid, such as hydrochloric or sulfuric acid to provide a suitable formfor development.

In coatings designed for dry processing with heat, the quantity ofavailable alkali for activating developing agents present is very loweven in the presence of socalled alkali generating compounds.Furthermore, the use of such alkali generating compounds is in somecases undesirable due to the problems of instability in the coatings.Thus, neutralized developer salts, such as neutralized'N-methyl-p-aminophenol is usually not suitable in coatings alone as adeveloping agent except when activated by significant concentrations ofalkali.

There has accordingly been a continuing need for components, especiallydeveloping agent precursors, that (a) can be employed in photographicsystems, especially photographic coatings, and be easily activated byheat with out the need of a separate alkali generating compound orseparate source of alkali, (b) provide an acidic developing agent, suchas a 3,4-dihydroxy furan silver halide developing agent or ahydroxytetronic silver halide developing agent, (c) and have substantialstability under conditions of storage and usage without causingundesired sensitometric properties.

It is accordingly an object of the present invention to provide improvedphotographic elements, compositions and processes employing developingagent precursors which are activated by heat without the need of aseparate alkali generating compound or alkali.

It is also an object of the invention to provide photographic emulsionscontaining such developing agent precursors which can be suitably storedand do not lose desired sensitometric properties under conditions ofstorage and use.

SUMMARY OF THE INVENTION In accordance with the invention, a stable,developing agent precursor which is a reaction product of (a) a 3,4-dihydroxy furan silver halide developing agent, such as ascorbic acid,or a hydroxytetronic acid silver halide developing agent, such as5-phenyl-3-hydroxytetronic acid, with (b) a basic aminophenol silverhalide developing agent employed in photographic elements, compositionsand processes, especially dry processes, has the property of being heatactivated in the absence of alkali and/or alkali generating materials.The developing agent precursors of the invention are suitable for dryprocessing, thus eliminating the need for any developer solutions oralkali normally employed to activate developing agents.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The exact nature of thedeveloping agent precursors of the invention is not fully understood. Itis believed a reaction product of (a) a 3,4-dihydroxy furan silverhalide developing agent or a hydroxytetronic acid silver halidedeveloping agent with (b) a basic aminophenol silver halide developingagent is in some complex or associated form.

The described developing agent precursors are typically prepared byreacting a 3,4-dihydroxy furan silver halide developing agent or ahydroxytetronic acid silver halide developing agent with an aminophenolsilver halide developing agent in basic or alkaline form. Thesecomponents are usually reacted in stoichiometric concentrations butconcentrations outside these can be employed. The reaction is normallycarried out under ambient conditions in a suitable solvent, such aswater, and the desired product is separated employing common separationtechniques. Preparation of a developing agent precursor which is thereaction product of ascorbic acid with N-methyl-paminophenol isexemplary of a suitable process for preparing developing agentprecursors of the invention. According to this process an aqueoussolution of sodium carbonate monohydrate and sodium sulfite is firstprepared. Ethyl acetate and a stoichiometric concentration ofN-methyl-p-aminophenol sulfate or hydrochloride is mixed into theaqueous sodium carbonate and sulfite solution andthe resulting two phasecomposition is vigorously mixed together. The mixture is then allowed toseparate into an upper and lower phase. The upper phase, which is anethyl acetate solution of basic N-rnethyl-paminophenol, is separated.This upper phase is added slowly to an aqueous methanol-ascorbic acidsolution containing a stoichiometric concentration of ascorbic acid. Theresulting solution is allowed to stand at ambient temperature andpressure until reaction completion producing a faint yellow coloredsolution. The desired reaction product is then separated by removing thesolvent from the reaction mixture by suitable means, such as a rotaryvacuum evaporator.

The described developing agent precursors can be prepared employingvarious 3,4-dihydroxy furan silver halide developing agents orhydroxytetronic acid silver halide developing agents which include:

3,4-dihydroxy furan developing agents or hydroxy tetronic aciddeveloping agents of the formula:

( E on A wide range of basic aminophenol developing agents can beemployed for preparing the described developing agents precursors. Basicaminophenol developing agents include such developing agents which arenot in an acid 4 salt form, e.g., are not in their hydrochloride orsulfate salt form. Suitable basic aminophenol developing agents employedin preparing the described developing agent precursors include, forexample, aminophenol developing agents of the formula:

OH I Rn R I N R1 wherein R and R are the same or different, and each ishydrogen or alkyl, e.g., alkyl containing 1 to 5 carbon atoms, such asmethyl, ethyl, propyl, butyl and pentyl; R and R are the same ordifferent, and each is hydrogen, alkoxy, e.g., alkoxy containing 1 to 5carbon atoms, such as methoxy, ethoxy, propoxy, butoxy and pentoxy,alkyl, as described, or amino, i.e., NH NHR or wherein R and R are alkylcontaining 1 to 5 carbon atoms, such as methyl, ethyl, propyl, butyl andpentyl; R and R are the same or different and each is hydrogen or alkyl,as described. Alkyl or aryl, as described, can include varioussubstituent groups which do not adversely alfect the properties of thedeveloping agent precursor, such as hydroxy or alkoxy, as described.

Examples of suitable basic aminophenol developing agents include:

Examples of other aminophenol developing agents are described, forinstance, in Mees and James, The Theory of the Photographic Process, 3rdedition (1966) pages 290- 291.

Suitable developing agent precursors which can be employed in thepractice of the invention include a reaction product of:

ascorbic acid with N-methyl-p-aminophenol,

ascorbic acid with N,N-diethyl-p-aminophenol,

ascorbic acid with Z-methyl-p-aminophenol,

ascorbic acid with N-ethyl-N-beta-hydroxyethyl-Z- methyl-p-aminophenol,

ascorbic acid with p-aminophenol, and/or 5-phenyl-3-hydroxytetronic acidwith N-methyl-paminophenol.

The described photographic developing agent precursors can be employedin any suitable location in a photographic system. They are typicallyemployed in one or more layers of a photographic element. Accordingly,one embodiment of the invention comprises an element comprising asupport and a developing agent precursor which is a reaction product of(a) a 3,4-dihydroxy furan silver halide developing agent, such asascorbic acid, or a hydroxytetronic acid silver halide developing agent,such as 5- phenyl-3-hydroxy-tetronic acid with (b) a basic aminophenolsilver halide developing agent, the reaction product having the propertyof being heat activated in the absence of alkali.

The described developing agent precursors can be em ployed in variouslayers of an element, e.g., in a photographic layer such as aphotographic silver salt emulsion layer, an overcoat layer, a layerunder the emulsion layer, a baryta layer, an antihalation layer or anylayer which provides the desired developing action upon heating of thedeveloping agent precursor.

According to this embodiment an element, especially a photographicelement, can comprise a support and a developing agent precursor whichis a reaction product of ascorbic acid with a basicN-methyl-p-aminophenol silver halide developing agent, the reactionproduct having the property of being heat activated in the absence ofalkali.

If desired, the described photographic developing agent precursors canbe employed in a photographic composition, such as a photographicemulsion. A further embodiment of the invention, accordingly, comprisesa photographic composition comprising a photographic silver salt and adeveloping agent precursor, which is a reaction product of (a) a3,4-dihydroxy furan silver halide developing agent or a hydroxytetronicacid silver halide developing agent, as described, with (b) a basicaminophenol silver halide developing agent, the reaction product havingthe property of being heat activated. in the absence of alkali.

The described developing agent precursors can be used in a Wide range ofphotographic emulsion. These precursors are useful in developing and/orincorporation in X-ray or other non-spectrally sensitized emulsions, orwith orthochromatic, panchromatic, infrared and other emulsions. Theycan also be employed with or in photographic emulsions containingspectral-sensitizing dyes, such as described in U.S. Pat. 2,526,632 ofBrooker et al. issued Oct. 24, 1950 and U.S. 2,503,776 of Sprague issuedApr. 11, 1950. Spectral sensitizers which can be used include cyanines,merocyanines, styryls and hemicyanines.

Various photographic salts, especially photographic Silver salts, can beused in the practice of the invention. These include photographic silverhalides, such as silver iodide, silver bromide, silver chloride, as wellas mixed halides, such as silver bromoiodide, silver chloroiodide, andthe like.

The described developing agent precursors can be incorporated inphotographic emulsions or layers of photographic elements using wellknown techniques in the photographic art. For example, they can bedissolved in a suitable solvent and added as such or they can be addedin the form of a dispersion. Techniques of this type are de scribed, forexample, in U.S. Pat. 2,322,027 of Jelley et al. issued June 15, 1943,and U.S. Pat. 2,801,171 of Fierke et al. issued July 30, 1957.

Coatings, especially photographic coatings, employed in the practice ofthe invention, are suitable on a wide variety of supports. Suitablesupports include those generally employed for photographic elements,such as various films including cellulose acetate films, cellulosenitrate films, polyethylene terephthalate films, or other polyesterfilms, polycarbonate films and related films or resinous materials; aswell as papers, such as paper supports coated with resinous materials,e.g., coated with polyethylene, polypropylene and/or ethylene-butenecopolymers; glass; metal, and the like. The supports and/or layerscoated on them can contain fluorescent brightening agents, such asstilbenes, benzothiazoles and benzoxazoles.

The photographic elements according to the invention typically containone or more layers comprising any of the known binding materialssuitable for photographic purposes. These include natural and syntheticbinding materials generally employed for this purpose, for example,gelatin, colloidal albumin, water-soluble vinyl polymers, such asmonoand poly-saccharides, cellulose derivatives, proteins, water-solublepolyacrylamides, polyvinyl pyrrolidone, and the like, as well asmixtures of such binding agents. These binding materials can alsocontain water-insoluble polymers, such as vinyl polymers, includingpolymers of acrylates and methacrylates, sulfoacrylates and the like.The elements can also contain stripping layers and/ or antistaticlayers.

Photographic emulsions employed in the practice of the invention can bechemically sensitized using any of the known procedures employed inemulsion making, such as by digesting with natural active gelatin orvarious sulfur, selenium, noble metal and/or gold compounds, and/ orwith reducing agents, such as stannous salts, polyamines and the like.

The developing agent precursors of the invention can be employed incombination with any silver halide developing agent. These can beemployed as the main developing agent, or as an auxiliary developingagent. Suitable silver halide developing agents which can be employed inthe practice of the invention include, for example, polyhydroxybenzenes,such as hydroquinone developing agents, e.g., hydroquinone, alkylsubstituted hydroquinones such as tertiary butylhydroquinone,methylhydroquinone and 2,5-dimethylhydroquinone; catechol andpyrogallol; chloro substituted hydroquinones such as chlorohydroquinoneor dichlorohydroquinone; alkoxy substituted hydroquinones such asmethoxyhydroquinone or ethoxyhydroquinone; aminophenol developing agentssuch as 2,4-diaminophenols, e.g., 2,4-diamino-6-methylphenol, andmethylaminophenols; hydroxylamines, such as N,N-di(2 ethoxyethyl)-amino;3 pyrazolidone developing agents, such as l-phenyl 3 pyrazolidone,including those described in British Pat. 930,572; and acyl derivativesof aminophenols, such as described in British Pat. 1,045,303. Suchdeveloping agents can be used alone or in combination when employed withthe described developing agent precursors.

The described developing agent precursors can be activated if desiredwith organic or inorganic alkali or alkali generating materials, e.g.,materials which release alkali upon heating. For example, the developingagent precursors can be activated with alkali metal hydroxides, such assodium hydroxide, potassium hydroxide or lithium hydroxide or alkalimetal carbonates, such as sodium carbonate or potassium carbonate orbicarbonates or with organic alkali, such as amines, guanidine oralkanol amines, such as ethylamine, ethanolamine or iminodiethanolamine.Alkali generating materials, which can be employed in combination withthe developing agent precursors, include those described in U.S. Pat.3,041,170 of Haist and King issued June 16, 1962; British Pat. 930,572published July 3, 1963; and Belgian Pat. 709,900. These include, forinstance, guanidinium salts and thiuronium alkane sulfonates which havethe property of releasing alkali upon heating to above about C., e.g.,about 90 C. to about 250 C. Examples of such materials include3-S-thiuronium propane sulfonate and betaisothioureidopropionic acid.Such compounds also have the advantage of stabilizing the resultingdeveloped image.

The described developing agent precursors are typically employed in oneor more layers of a photographic element, which, after exposure, isheated to cause desired development. Accordingly, a photographic elementof the invention is highly suitable for use in dry processing systems.It may, however, be employed in so-called wet processing systems, wherethe described photographic element is contacted with a suitableactivator such as an aqueous alkaline solution, such as an alkalinesolution of an alkali metal hydroxide, carbonate or organic alkali asdescribed.

The developing agent precursors employed in the practice of theinvention are stable and while present in one or more layers of aphotographic element subjected to ambient temperatures do not provideundesired sensitometric properties. However, at elevated temperatures,e.g., about 90 C. or higher, typically between about 90 C and about 250C., the developing agent precursor is activated to provide desireddeveloping action.

Accordingly, another embodiment of the invention com- .prises a methodof developing a latent image in a photographic element comprising asupport, an exposed photographic silver salt and a developing agentprecursor which is a reaction product of (a) a 3,4-dihydroxy rnransilver halide developing agent or a hydroxytetronic acid silver halidedeveloping agent with (b) a basic aminophenol silver halide developingagent, the reaction product having the property of being heat activatedin the absence of alkali, comprising heating the photographic element toa temperature at which the basic aminophenol silver halide developingagent is separated from the reaction product. Heating is normallycarried out at temperatures above about 90 C., preferably above about150 C., e.g., about 150 C. to about 250 C., at which temperature the developing agent precursor is activated.

Heating according to the invention can be carried out employing anysuitable heating means, such as by contacting the photographic elementwith heated rollers or plates, infrared lamps or other heating means.

The time for developing a desired image can vary depending upon severalfactors, such as the desired image, the particular components of thephotographic element, the specific developing agent precursor employedin the practice of the invention and the like. Generally, heating aphotographic element according to the invention for about 1 second toabout a minute or more is suitable.

It can be advantageous in some cases to employ an antifoggant in thepractice of the invention, such as in the photographic elementsdescribed. Suitable antifoggants, include organic antifoggants, such asbenzotriazole, benzimidazole, Z-mercaptobenzimidazole, andmercaptoazoles. An inorganic antifoggant, such as potassium bromide,potassium iodide and/or sodium bromide can be employed if desired. Asuitable concentration of antifoggant can vary depending upon thefactors described, but usually a concentration of less than about 2% byweight of antifoggant, e.g., 0.01 to 2% by weight is suitable.

The described silver halide emulsions can also contain antifoggants,such as azaindenes, 4-thiazoline-2- thiones and their related2,2'-dithio-bisthiazoles, 4-hydroxythiazolidiue-Z-thiones and theirrelated dithiocarbamates, monothioor dithio-urazoles, e.g., the alkyl,aryl, acylated, or aroylated derivatives,Z-thiobenzthiazolyl-substituted napthohydroquinones, 4 thiopyrirnidines,4,4-dithio-bispyrimidines, enamineacyl isot-hiocyanates, substitutedpyrimidines, e.g., 2-thio and 4-thio derivatives (preferably saidpyrimidines or isocyanates being in combination with a tetraazaindene),and organo lead compounds, e.g., trial-kyl-N-contaming-heterocyclic leador triarylalkylthio (or arylthio) lead derivatives. Nitro-substitutedheterocyclic compounds, preferably the cyanine and merocyanine dyederivatives, e.g., 1,3-diethyl-6-nitrothia-2-cyanine, are also useful asantifoggants in photographic silver halide photographic emulsionsparticularly processed in a hardening developer.

When the described developing agent precursors are employed inphotographic elements they can be employed in a wide range ofconcentrations. Normally concentrations of about 0.25 to about 4.0 molesof developing agent precursor per mole of silver present in thephotographic element is suitable.

Other heat activatable developers or developing agent precursors can beemployed in the practice of the invention, e.g., in the describedphotographic elements and compositions. For example, a heat activatabledeveloper can be prepared by reactivating an aminophenol developingagent such as N-methyl-p-aminophenol With a sulfite or bisulfitecompound, such as sodium sulfite or sodium bisulfite to form a reactionproduct which can be em- 8 ployed as a component of the systemdescribed. Such reaction products are useful in photographic elementsand/or compositions for dry processing.

Other developing agents or developing agent precursors which can beemployed in photographic elements, compositions or processes asdescribed include reaction products of ascorbic acid silver halidedeveloping agents with 3-pyrazolidone developing agents, such as3-pyrazolidone developing agents described in British Pat. 930,572,e.g., 1-phenyl-3-pyrazolidone or l-phenyl-4,4-dimethyl- 3-pyrazolidone;or reaction products of a polyhydroxybenzene developing agent, such ashydroquinone, catechol, 4-phenylcatechol or tertiary-butylhydroquinonewith a 3-pyrazolidone developing agent as described. These are useful inany suitable location in the described photographic systems and areespecially suitable for dry processing.

The following examples are included for a further understanding of theinvention.

EXAMPLE 1 This example illustrates preparation of developing agentprecursors of the invention.

50 grams of sodium carbonate monohydrate and 30 grams of sodium sulfiiteare sequentially added to 500 milliliters of distilled water in a flask.The admixture is stirred until the components are dissolved. 500milliliters of ethyl acetate and 50 grams of N-methyl-p-aminophenolsulfate are sequentially added to the flask. The solution is thenvigorously agitated. Two phases are formed. The phases formed areseparated using a separatory funnel. The upper phase comprising ethylacetate and N-methyl-p-aminophenol is retained.

52 grams of ascorbic acid is added to 200 milliliters of ethanol and 20milliliters of distilled water in a beaker. The mixture is stirred untila solution is formed. Next, the ethyl acetate phase containingN-methyl-p-aminophenol, previously prepared, is slowly added to theascorbic acid solution. The solution is allowed to stand. The solvent inthe mixture is then removed employing a rotary vacuum evaporator. Theresulting liquid is yellow-orange in color, and comprises a complex ofascorbic acid with N-methyl-p-aminophenol.

EXAMPLE 2 A photographic composition is prepared by mixing the followingcomponents:

Ingredient: Concentration Sucrose g 1.5 Citric acid g 0.2 Distilledwater g 20.0 Gelatin, 5 by Weight aqueous solution rnl 20.0 Ascorbicacid-N-methyl-p-aminophenol complex (as prepared in Example 1) ml 1.6Silver chloride emulsion 1 rnl 2.0

1A fine grain silver chloride emulsion comtaining one mole of silver pergrams of gelmtin in each 2.5 kg. of emulsion.

A small concentration of saponin (2% by weight) is added to theresulting composition as a coating aid and the mixture is filtered. Theresulting composition is then coated on a paper support at a Wetthickness of 0.006 inch. The resulting photographic element is thendried.

EXAMPLE 3 The procedure set out in Example 2 is repeated with theexception that a polyethylene terephthalate film base is employed inplace of the paper support.

9 EXAMPLE 4 A strip of the photographic paper prepared as described inExample 2 is sensitometrically exposed and the side opposite thephotographic coating is contacted with a heated block having a surfacetemperature of 155 C. for a period of 30 seconds.

A dark brown image having good density with a tannish background isproduced.

EXAMPLE 5 A strip of the photographic element as described in Example 3is sensitometrically exposed. The element is then heated by placing theside opposite the photographic coating in contact with a heated blockhaving a surface temperature of 155 C. for a period of seconds.

A dark brown image of good density with a tannish background isproduced.

EXAMPLE 6 This is a comparative example.

A photographic element is prepared as described in Example 2 with theexception that 0.8 gram of N-methylp-aminophenol sulfate and 0.8 gram ofascorbic acid is used in place of 1.6 milliliters of a complex asprepared in Example 1, i.e., in place of a complex of ascorbic acid withN-methyl-p-aminophenol.

The resulting photographic element is dried and sensitometricallyexposed. It is then heated by passing the side opposite the photographiccoating over a heated block having a surface temperature of 155 C. for aperiod of 30 seconds.

An extremely brownish image with an orange background is produced. Incomparison to the photographic elements prepared and processed accordingto the invention, a very poor image is obtained with photographiccoatings containing the described individual developing agents.

EXAMPLE 7 This illustrates that the developing agent precursorsdescribed can be employed in solutions for so-called wet processing.

49 grams of N-methyl-p-aminophenol sulfate is added to 500 millilitersof distilled water in a beaker. The mixture is heated to a temperatureof 60 C. to form a solution. Then 31 grams of ascorbic acid is added tothe solution with stirring. Then 12.5 grams of sodium carbonatemonohydrate is added with stirring to the resulting solution. Themixture is cooled by the addition of refrigerated water to a temperatureof 9 C. and is permitted to stand for a period of one hour. Small whitecrystals of the desired reaction product, which is a complex of ascorbicacid with N-methyl-p-aminophenol precipitate from the solution and areremoved by filtration. The crystals are then dried.

One gram of the described white crystals is mixed into 50 milliliters ofdistilled water to form a heat activatable developing agent precursorsolution.

A strip of exposed fine grain photographic film is sensitometricallyexposed with a commercial sensitometer and then placed in the resultingsolution for 5 minutes at 24 C. No visible image is formed.

The developer precursor solution is then heated to about its boilingtemperature for a period of 90 seconds. A second strip of identical finegrain photographic film is sensitometrically exposed and placed in thesolution which is at a temperature of 80 C. A visible image is formed inabout 2 minutes consisting of finely divided brownish silver of lowdensity.

The developing solution is then cooled to a temperature of 24 C. and athird strip of photographic film (Kodak Panatomic-X Film) issensitometrically exposed and placed in the solution for a period of 5minutes. No visible image is formed.

This illustrates the developing agent precursors em- 10 ployed in thepractice of the invention can be employed in developer compositionswhich are heat activated.

EXAMPLE 8 A photographic element is prepared as described in Example 2with the addition of 2 g. of 3-S-thiuroniumpropane sulfonate to thedescribed composition.

The element is sensitometrically exposed and heated as described inExample 4 to produce a developed lightstable image.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:

1. A photographic silver halide element comprising a support and adeveloping agent precursor which is a reaction product of (a) a3,4-dihydroxy furan silver halide developing agent or a hydroxytetronicacid silver halide developing agent With (b) a basic aminophenol silverhalide developing agent, said reaction product having the property ofbeing heat activated in the absence of alkali.

2. An element as in claim 1 also comprising a thiuronium alkanesulfonate.

3. An element as in claim 1 comprising a support and a developing agentprecursor which is a reaction product of ascorbic acid with a basicN-methyl-p-aminophenol silver halide developing agent, said reactionproduct having the property of being heat activated in the absence ofalkali.

4. A photographic element as in claim 1 comprising a support, sucrose,citric acid, a reaction product of ascorbic acid with anN-methyl-p-aminophenol silver halide developing agent and photographicsilver halide emulsion.

S. A photographic composition comprising a photographic silver halideand a developing agent precursor Which is a reaction product of (a) a3,4-dihydroxy furan silver halide developing agent or a hydroxytetronicacid silver halide developing agent with (b) a basic aminophenol silverhalide developing agent, said reaction product having the property ofbeing heat activated in the absence of alkali.

6. A photographic composition as in claim 5 wherein said developingagent precursor is a reaction product of ascorbic acid with a basicN-methyl-p-aminophenol silver halide developing agent.

7. A photographic composition as in claim 6 comprising a photographicsilver halide emulsion.

8. A photographic composition as in claim 5 comprising sucrose, citricacid, a reaction product of ascorbic acid with an N-methyl-p-aminophenolsilver halide developing agent and photographic silver halide emulsion.

9. A method of developing a latent image in a photographic elementcomprising a support, an exposed photographic silver halide and adeveloping agent precursor which is a reaction product of (a) a3,4-dihydroxy furan silver halide developing agent or a hydroxytetronicacid silver halide developing agent with (b) a basic aminophenol silverhalide developing agent, said reaction product having the property ofbeing heat activated in the absence of alkali, comprising heating thephotographic element to a temperature at which the basic aminophenolsilver halide developing agent is separated from the reaction product.

10. A method as in claim 9 wherein the developing agent precursor is areaction product of ascorbic acid with a basic N-methyl-p-aminophcnolsilver halide developing agent.

11. A method as in claim 9 comprising heating the element to at leastabout C.

12. A method as in claim 9 of developing a latent image in aphotographic element comprising a support, sucrose,

11 citric acid, a reaction product of ascorbic acid with anN-methyl-p-arninophenol silver halide developing agent and photographicsilver halide emulsion comprising heating said element to 90 C. to 250C. for about 1 second to about 1 minute.

13. A method of developing a latent image in a photographic elementcomprising a support, an exposed photographic silver halide and adeveloping agent precursor which is a reaction product of (a) a3,4-dihydroxy furan silver halide developing agent or a hydroxytetronicacid silver halide developing agent with (b) a basic aminophenol silverhalide developing agent, comprising contacting the element with analkaline development activator.

14. A photographic developer precursor composition comprising a neutralor acidic aqueous solution of a reaction product of a 3,4-dihydroxyfuran silver halide developing agent or a hydroxytetronic acid silverhalide developing agent with a basic aminophenol silver halidedeveloping agent, the composition having the property of being activewith the application of heat.

15. A photographic developing agent precursor comprising a reactionproduct of (a) a 3,4-dihydroxy furan silver halide developing agent or ahydroxytetronic acid silver halide developing agent with (b) a basicaminophenol silver halide developing agent, said developing agentprecursor having the property of being activated in the absence ofalkali.

12 16. A photographic developing agent precursor as in claim 15comprising a reaction product of ascorbic acid with anN-methyl-p-aminophenol silver halide developing agent.

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